Electromagnetic switch for sliding shoe sorter conveyor system utilizing reversed current flow in electromagnet coil

ABSTRACT

A method, electromagnetic switch, controller and program product, when energizing an electromagnetic coil to urge a selected shoe into a diverting path downstream of the electromagnetic switch, reverse current flow during at least a portion of the time that the electromagnetic coil is energized to recover energy from the electromagnetic coil.

BACKGROUND

Conveyor systems are extensively used for various purposes, including,for example, in various manufacturing, packaging, shipping anddistribution facilities. One particular use of some types of conveyorsystems is in the sortation of packages and other articles carried fromone or more sources to various different destinations. Sliding shoesorter conveyor systems, for example, generally incorporate a primaryconveyor including a series of rails that both serve as the supportsurface for conveyed articles as well as allow for the transversemovement (i.e., movement transverse to the movement of the conveyorsurface) of pushing components commonly referred to as shoes to divertsupported articles toward desired destinations by selectively “pushing”the supported articles off the side of the primary conveyor, e.g., ontoa secondary conveyor or an inclined surface.

In some sliding shoe sorter conveyor systems, shoes are provided withstructures (e.g., pins and/or bearings) disposed below the uppersurfaces of the rails that are guided along a desired path to controlthe transverse positions of the shoes along the rails. While an articleis being conveyed by the conveyor on one or more rails, the shoes onthose rails are generally oriented proximate one of the sides of theconveyor and out of contact with the articles, in many cases usingguides or channels that run along the underside of the conveyor surfaceand guide the pins and/or bearings of the shoes. At various points alongthe length of the conveyor where it may be desirable to divert articlesto particular destinations, additional angled guides or channels aregenerally provided underneath the conveyor surface to guide the pinsand/or bearings of shoes such that the shoes are moved from one side ofthe conveyor to the other as the rails upon which they are supportedadvance along the conveyor. By doing so, the shoes themselves are ableto push any articles supported on the rails off the side of the conveyorand to a desired destination.

In order to selectively divert articles, an electromechanical componentreferred to as a switch is generally positioned underneath the conveyorsurface upstream of each angled guide or channel to selectively divertshoes toward the angled guides or channels. While some switchesincorporate movable mechanical components that route the pins and/orbearings of shoes from an input path to either a non-diverting path or adiverting path, other switches referred to herein as electromagneticswitches utilize magnetics for routing purposes, such that magneticfields are used to draw the pins and/or bearings of shoes towards one ofthe non-diverting or diverting paths.

Electromagnetic switches are generally quieter and more reliable thanmechanical switches due to the use of fewer moving parts. Nonetheless,electromagnetic switches generally require a substantial amount ofelectrical power to operate, and particularly at higher conveyor speeds(e.g., conveyor speeds in excess of about 350 feet per minute, arerequired to generate sufficiently strong magnetic fields in order toreliably divert shoes in the very limited time frame through which theypass through the switch. The electromagnetic coils in some switchdesigns, in particular, may generate substantial heat and may havereduced reliability as a result.

Therefore, a continuing need exists in the art for an efficient andreliable electromagnetic switch design for use with sliding shoe sorterconveyor systems.

SUMMARY

The invention addresses these and other problems associated with the artby providing a method, electromagnetic switch, controller and programproduct that, when energizing an electromagnetic coil to urge a shoeinto a diverting path downstream of the electromagnetic switch, reversecurrent flow during at least a portion of the time that theelectromagnetic coil is energized to recover energy from theelectromagnetic coil.

Therefore, consistent with one aspect of the invention, a method ofdiverting a shoe on a conveyor with an electromagnetic switch configuredto selectively direct the shoe from an input path to one of anon-diverting path and a diverting path may include energizing anelectromagnetic coil of the electromagnetic switch to generate amagnetic field urging the shoe towards the diverting path, whereenergizing the electromagnetic coil includes supplying an electricalcurrent to the electromagnetic coil, and while generating the magneticfield with the electromagnetic coil, alternating between supplyingelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil to recover energy from theelectromagnetic coil.

Some embodiments may also include receiving a direct current voltageacross first and second power input terminals, where the electromagneticcoil includes first and second coil terminals, and alternating betweensupplying the electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil includesswitching a drive circuit between a first state in which the first andsecond power input terminals are electrically coupled respectively tothe first and second coil terminals of the electromagnetic coil and asecond state in which the first power input terminal is electricallycoupled to one of the second and first coil terminals of theelectromagnetic coil to receive current flow from the electromagneticcoil.

Also, in some embodiments, the drive circuit includes an H-bridgecircuit that couples the first and second power input terminals to thefirst and second coil terminals of the electromagnetic coil. Further, insome embodiments, the H-bridge circuit includes first and second legscoupled in parallel to one another and coupled across the first andsecond power input terminals, the first leg including a first switchcoupled between the first power input terminal and the first coilterminal and a second switch coupled between the second power inputterminal and the first coil terminal, and the second leg including athird switch coupled between the first power input terminal and thesecond coil terminal and a fourth switch coupled between the secondpower input terminal and the second coil terminal, where when in thefirst state, the first and fourth switches are closed and the second andthird switches are open such that the first coil terminal is coupled tothe first power input terminal through the first switch and the secondcoil terminal is coupled to the second power input terminal through thefourth switch.

In some embodiments, when in the second state, the first switch isclosed and the second, third and fourth switches are open such that thefirst power input terminal is coupled to the first coil terminal throughthe first switch and the second power input terminal is electricallyisolated from the first and second coil terminals. In addition, in someembodiments, when in the second state, the second and third switches areclosed and the first and fourth switches are open such that the firstcoil terminal is coupled to the second power input terminal through thesecond switch and the second coil terminal is coupled to the first powerinput terminal through the third switch. In some embodiments, each ofthe first, second, third, and fourth switches includes a respectivefirst, second, third and fourth MOSFET.

In addition, in some embodiments, each of the first, second, third, andfourth MOSFETs includes an N-channel MOSFET and includes a gate, a drainand a source, and each of the first, second, third, and fourth switchesfurther includes a respective reverse biased diode coupled between thedrain and the source thereof, and the drains of the first and thirdMOSFETs are coupled to the first power input terminal, the sources ofthe second and fourth MOSFETs are coupled to the second power inputterminal, the source of the first MOSFET and the drain of the secondMOSFET are coupled to the first coil terminal and the source of thethird MOSFET and the drain of the fourth MOSFET are coupled to thesecond coil terminal. Moreover, in some embodiments, switching betweenthe first and second states includes driving the gates of the first andfourth MOSFETs during the first state to close the first and fourthswitches. In some embodiments, switching between the first and secondstates includes driving only the gate of the first MOSFET during thesecond state to close the first switch.

Moreover, in some embodiments, switching between the first and secondstates includes driving the gates of the second and third MOSFETs duringthe second state to close the second and third switches. In someembodiments, reversing current flow through the electromagnetic coil torecover energy from the electromagnetic coil includes storing energyrecovered from the electromagnetic coil in at least one capacitor. Inaddition, in some embodiments, the at least one capacitor is coupledacross the first and second power input terminals. In some embodiments,the at least one capacitor is disposed in a power supply coupled acrossthe first and second power input terminals.

Some embodiments may further include, during a first portion of theenergization of the electromagnetic coil, driving the electromagneticcoil to a peak current, and alternating between supplying the electricalcurrent to the electromagnetic coil and reversing current flow throughthe electromagnetic coil is performed during a second portion of theenergization of the electromagnetic coil to drive the electromagneticcoil with a hold-on current. Also, in some embodiments, the hold-oncurrent is less than the peak current. In some embodiments, the hold-oncurrent is about 75 percent of the peak current.

In addition, some embodiments may also include sensing a portion of theshoe approaching the electromagnetic switch, and determining a starttime of the first portion of the energization of the electromagneticcoil in response to sensing the portion of the shoe approaching theelectromagnetic switch to cause the electromagnetic coil to reach thepeak current while the portion of the shoe is adjacent theelectromagnetic coil. Also, in some embodiments, sensing the portion ofthe shoe approaching the electromagnetic switch includes determining aspeed of the shoe approaching the electromagnetic switch. Moreover, insome embodiments, determining the speed of the shoe approaching theelectromagnetic switch includes sensing the portion of the shoeapproaching the electromagnetic switch at multiple positions.

Further, in some embodiments, the portion of the shoe includes a pin anda bearing, and sensing the portion of the shoe approaching theelectromagnetic switch at multiple positions includes sensing one of thepin and the bearing at a first position among the multiple positions andsensing one of the pin and the bearing at a second position among themultiple positions. Some embodiments may also include determining aduration of each of the first and second portions of the energization ofthe electromagnetic coil in response to sensing the portion of the shoeapproaching the electromagnetic switch. Some embodiments may furtherinclude determining a frequency of alternating between supplying theelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil in response to sensing the portionof the shoe approaching the electromagnetic switch. Some embodiments mayalso include determining a number of cycles to alternate betweensupplying the electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil in response tosensing the portion of the shoe approaching the electromagnetic switch.

Consistent with another aspect of the invention, an electromagneticswitch for selectively directing a shoe on a conveyor from an input pathto one of a non-diverting path and a diverting path may include anelectromagnetic coil, and a drive circuit coupled to the electromagneticcoil, the drive circuit configured to energize the electromagnetic coilto generate a magnetic field urging the shoe towards the diverting path,where the drive circuit is further configured to, during energization ofthe electromagnetic coil, alternate between supplying electrical currentto the electromagnetic coil and reversing current flow through theelectromagnetic coil to recover energy from the electromagnetic coil.

In some embodiments, the drive circuit includes first and second powerinput terminals across which is supplied a direct current voltage, theelectromagnetic coil includes first and second coil terminals, and thedrive circuit is configured to alternate between supplying theelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil by switching between a first statein which the first and second power input terminals are electricallycoupled respectively to the first and second coil terminals of theelectromagnetic coil and a second state in which the first power inputterminal is electrically coupled to one of the second and first coilterminals of the electromagnetic coil to receive current flow from theelectromagnetic coil.

Also, in some embodiments, the drive circuit includes an H-bridgecircuit, the H-bridge circuit including first and second legs coupled inparallel to one another and coupled across the first and second powerinput terminals, the first leg including a first switch coupled betweenthe first power input terminal and the first coil terminal and a secondswitch coupled between the second power input terminal and the firstcoil terminal, and the second leg including a third switch coupledbetween the first power input terminal and the second coil terminal anda fourth switch coupled between the second power input terminal and thesecond coil terminal, where when in the first state, the drive circuitcloses the first and fourth switches and opens the second and thirdswitches such that the first coil terminal is coupled to the first powerinput terminal through the first switch and the second coil terminal iscoupled to the second power input terminal through the fourth switch.

In some embodiments, when in the second state, the first switch isclosed and the second, third and fourth switches are open such that thefirst power input terminal is coupled to the first coil terminal throughthe first switch and the second power input terminal is electricallyisolated from the first and second coil terminals. Further, in someembodiments, when in the second state, the second and third switches areclosed and the first and fourth switches are open such that the firstcoil terminal is coupled to the second power input terminal through thesecond switch and the second coil terminal is coupled to the first powerinput terminal through the third switch.

In some embodiments, each of the first, second, third, and fourthswitches includes a respective first, second, third and fourth N-channelMOSFET and includes a gate, a drain and a source, and each of the first,second, third, and fourth switches further includes a respective reversebiased diode coupled between the drain and the source thereof, and thedrains of the first and third N-channel MOSFETs are coupled to the firstpower input terminal, the sources of the second and fourth N-channelMOSFETs are coupled to the second power input terminal, the source ofthe first N-channel MOSFET and the drain of the second N-channel MOSFETare coupled to the first coil terminal and the source of the thirdN-channel MOSFET and the drain of the fourth N-channel MOSFET arecoupled to the second coil terminal.

Further, in some embodiments, the drive circuit is configured to switchbetween the first and second states by driving the gates of the firstand fourth N-channel MOSFETs during the first state to close the firstand fourth switches. Also, in some embodiments, the drive circuit isconfigured to switch between the first and second states by driving thegates of the first and fourth MOSFETs during the first state to closethe first and fourth switches. In addition, in some embodiments, thedrive circuit is configured to switch between the first and secondstates by driving only the gate of the first MOSFET during the secondstate to close the first switch.

Some embodiments may also include a power supply coupled across thefirst and second power input terminals and at least one capacitorconfigured to store energy recovered from the electromagnetic coil whenin the second state. In addition, some embodiments may also include acontroller coupled to the drive circuit and configured to, during afirst portion of the energization of the electromagnetic coil, cause thedrive circuit to drive the electromagnetic coil to a peak current, andduring a second portion of the energization of the electromagnetic coil,cause the drive circuit to alternate between supplying the electricalcurrent to the electromagnetic coil and reversing current flow throughthe electromagnetic coil with a hold-on current that is less than thepeak current.

In addition, some embodiments may further include one or more sensorsconfigured to sense a portion of the shoe approaching theelectromagnetic switch, and the controller is configured to determine astart time of the first portion of the energization of theelectromagnetic coil in response to sensing of the portion of the shoeapproaching the electromagnetic switch by the one or more sensors tocause the electromagnetic coil to reach the peak current while theportion of the shoe is adjacent the electromagnetic coil. In addition,in some embodiments, the one or more sensors includes multiple sensorsdisposed at multiple positions, and the controller is further configuredto determine a speed of the shoe approaching the electromagnetic switchin response to the sensing of the portion of the shoe approaching theelectromagnetic switch by the one or more sensors.

In some embodiments, the portion of the shoe includes a pin and abearing, and the multiple sensors includes a first sensor disposed at afirst position and configured to sense one of the pin and the bearingand a second sensor disposed at a second position and configured tosense one of the pin and the bearing. Further, in some embodiments, thecontroller is further configured to determine a duration of each of thefirst and second portions of the energization of the electromagneticcoil in response to the sensing of the portion of the shoe approachingthe electromagnetic switch by the one or more sensors. In addition, insome embodiments, the controller is further configured to determine afrequency of alternating between supplying the electrical current to theelectromagnetic coil and reversing current flow through theelectromagnetic coil in response to the sensing of the portion of theshoe approaching the electromagnetic switch by the one or more sensors.Further, in some embodiments, the controller is further configured todetermine a number of cycles to alternate between supplying theelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil in response to the sensing of theportion of the shoe approaching the electromagnetic switch by the one ormore sensors.

Consistent with another aspect of the invention, a controller for anelectromagnetic switch configured to selectively direct a shoe on aconveyor from an input path to one of a non-diverting path and adiverting path may include one or more processors, and program codeexecutable by the one or more processors to energize an electromagneticcoil of the electromagnetic switch to generate a magnetic field urgingthe shoe towards the diverting path, where the controller is configuredto energize the electromagnetic coil by causing an electrical current tobe supplied to the electromagnetic coil, and while the electromagneticcoil is energized to generate the magnetic field, alternate betweencausing the electrical current to be supplied to the electromagneticcoil and causing current flow to be reversed through the electromagneticcoil to recover energy from the electromagnetic coil.

These and other advantages and features, which characterize theinvention, are set forth in the claims annexed hereto and forming afurther part hereof. However, for a better understanding of theinvention, and of the advantages and objectives attained through itsuse, reference should be made to the Drawings, and to the accompanyingdescriptive matter, in which there is described example embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of a sliding shoe sorter conveyor systemincorporating an electromagnetic switch consistent with some embodimentsof the invention.

FIG. 2 is a top perspective view of one example implementation of theelectromagnetic switch of FIG. 1.

FIG. 3 is a cross-sectional view taken along lines 3-3 of FIG. 2.

FIG. 4 is a bottom perspective view of the electromagnetic switch ofFIG. 2.

FIG. 5 is a top plan view of the electromagnetic switch of FIG. 2, andfunctionally illustrating multiple positions of a shoe as it passesthrough the electromagnetic switch.

FIG. 6 is a block diagram of an example implementation of a controlsystem suitable for use in controlling the electromagnetic switch ofFIG. 2.

FIG. 7 is an example timing diagram suitable for use by the controlsystem of FIG. 6.

FIG. 8 is a flowchart illustrating an example sequence of operations forcontrolling the electromagnetic switch using the control system of FIG.6.

DETAILED DESCRIPTION

Turning to the drawings, wherein like numbers denote like partsthroughout the several views, FIG. 1 illustrates a sliding shoe sorterconveyor system 100 suitable for implementing the various conceptsdisclosed herein. Sliding shoe sorter conveyor system 100 in theillustrated embodiment includes a primary conveyor 102 and a secondaryconveyor 104 representing a destination or diversion point to whichvarious articles (e.g., articles 106, 108, 110 illustrated in FIG. 1)may be selectively diverted. Articles 106, 108, 110 are supported on aconveyor surface defined in the illustrated embodiment by a plurality ofrails 112, and a plurality of shoes 114 are slidably supported by therails 112 to selectively divert articles to selected destinations ordiversion points along primary conveyor 102. In the illustratedembodiment, shoes 114 are normally maintained to one side of theconveyor (e.g., along right side 116 or left side 118, where “right” and“left” are relative to the direction of conveyance for primary conveyor102), and generally are not in contact with any articles while in thisnon-diverting position. Then, whenever it is desirable to divert anyarticle (e.g., article 108 illustrated in FIG. 1), one or more shoes(e.g., shoes 114 a illustrated in FIG. 1) are selectively diverted alonga diverting path by an electromagnetic switch 120 to both contact andpush the article laterally or transversely across the width of theprimary conveyor and to the destination or diversion point (e.g.,secondary conveyor 104 illustrated in FIG. 1).

In some embodiments, shoes 114 may be maintained to one side of primaryconveyor 102 unless they are diverting an article and may return to thesame side once the article has been diverted. In other embodiments,however, shoes may be capable of diverting articles to destinations oneither side of primary conveyor 102, and thus shoes may be capable ofbeing maintained on either side of the primary conveyor and selectivelydiverted to the opposite side in some embodiments. It will also beappreciated that a destination or diversion point to which shoes maydivert an article may be another conveyor, an inclined surface, a bin,or any other suitable mechanism or receptacle for receiving divertedarticles.

As noted above, shoes 114 are supported on rails 112, which in theillustrated embodiment are generally formed of extruded aluminum. Itwill be appreciated that sliding shoes may be used in connection withother types of conveyors, as well as with different types of railsand/or rails with different profiles and/or different materials. Othervariations will be apparent to those of ordinary skill having thebenefit of the instant disclosure.

FIGS. 2-5 illustrate an example implementation of electromagnetic switch120 in greater detail. Electromagnetic switch 120 is supported between apair of cross braces 122 that support the conveyor, and a switch body124 is supported on a pair of spacer isolating rubber mounts 126. A pinguide 128 serves as an input path to the switch, with a non-divertingpin guide 130 serving as a non-diverting path and a divert guide angle132 serving as a diverting path for the switch. Shoes 114 are thusreceived at the input path (pin guide 128) and either guided to thenon-diverting path (non-diverting pin guide 130) or diverted to thediverting path (divert guide angle 132). While not shown in FIG. 2,divert guide angle 132 generally extends at an angle to the direction ofconveyance to the opposite side of the conveyor to thereby guide shoesto the opposite side of the conveyer, where they are generally receivedby a pin guide (not shown) that extends generally parallel to thedirection of conveyance.

With additional reference to FIG. 3, each shoe 114 includes a pusherbody 134 formed of urethane or another pliable material and supported ona receiver 136 that is configured to slidably support the shoe betweenpairs of adjacent rails 112 (FIG. 1). A pin 138 extends through body 134and receiver 136 and projects downwardly to be received in each pinguide, with a bearing 140 rotatably supported on pin 138. Pin 138 andbearing 140 are desirably formed of a ferromagnetic material such assteel, and as will be discussed in greater detail below, switch 120selectively applies multiple magnetic fields to urge pin 138 and bearing140 toward one of the diverting path and the non-diverting path for theswitch.

A sensor mounting block 142 supports one or more sensors configured tosense a portion of each shoe 114 approaching switch 120. In theillustrated embodiment, the one or more sensors includes multiplesensors disposed at multiple positions to enable both a position and aspeed of a shoe to be determined. Further, in the illustratedembodiment, the multiple sensors include a pin sensor 144 and a bearingsensor 146 that respectively sense the pin 138 and bearing 140 atdifferent positions. Each of sensors 144, 146 may be implemented in someembodiments using photo-eyes or other optical sensors, although otherpresence detecting, position and/or speed sensors may be used in otherembodiments.

In still other embodiments, as few as one sensor or more than twosensors may be used, and it will be appreciated that each sensor maysense the pin, the bearing, or some other portion of each shoe.Therefore, the invention is not limited to the specific sensorsillustrated herein.

Switch 120 also includes a pair of electromagnetic coils 148, 150, alsoreferred to herein as upstream and downstream electromagnetic coils,respectively, supported by a magnet mount 152. Electromagnetic coil 148is considered to be upstream relative to electromagnetic coil 150, whileelectromagnetic coil 150 is configured to be downstream relative toelectromagnetic coil 148, and it should be appreciated that the terms“upstream” and “downstream,” as used in this application, are intendedto define positions and movement relative to the direction movement of ashoe through switch 120, with downstream referring to the direction ofmovement of a shoe within switch 120 (generally from left to right inFIG. 2) and upstream referring to the opposite direction therefrom(generally from right to left in FIG. 2).

A guide block 154 is disposed opposite coils 148, 150 to define achannel through which the pin and bearing of each shoe passes, anddownstream of coils 148, 150 on opposite sides of the channel aredisposed a divert permanent magnet 156 and a non-divert permanent magnet158. As will become more apparent below, whenever it is desirable todivert a shoe into the diverting path, coils 148, 150 are energized tosubject the pin and bearing of the shoe to magnetic fields that urge thepin and bearing toward the coils, and desirably to position the pin andbearing adjacent the divert permanent magnet 156 as the shoe continuesto move through the switch such that the magnetic field generated by thedivert permanent magnet 156 engages the pin and bearing and directs theshoe into the diverting path. In contrast, when coils 148 and 150 arenot energized, the pin and bearing of a non-diverted shoe will generallycontinue along the channel between the coils and guide block 154, andnon-divert permanent magnet 158 is positioned to engage the pin andbearing of the non-diverted shoe to assist in guiding the shoe into thenon-diverting path of the switch.

In the illustrated embodiment, each of permanent magnets 156, 158 isconfigured as a stack arrangement of ferromagnetic plates such as steelplates interleaved with non-ferromagnetic cage plates constructed ofaluminum or a polymer material, and including apertures within which arereceived a plurality of rare earth magnets. It will be appreciated thatthe size, number and types of magnets, number and types of plates, etc.of each magnet 156, 158 may be varied in different embodiments, e.g., totailor each magnet to provide a desired strength and orientation ofmagnetic field (e.g., about 15 pounds of force for each magnet in someembodiments). In addition, in some embodiments one or both of magnets156, 158 may be omitted or substituted with one or more electromagnets.Therefore, the invention is not limited to the particular combinationand orientation of electromagnetic coils and permanent magnetsillustrated in FIG. 2.

As will become more apparent below, however, it is desirable in someembodiments to utilize a pair of coils 148, 150 and a downstreampermanent magnet 156 to pull both the bearing and the pin of each shoeto be diverted into a diverting path, and to do so in a manner in whichthe energizing sequence of the coils is distributed over substantially afull pitch between shoes, which can lower peak current draw and spreadoverall energy consumption out over a longer period of time, and therebylower overall power draw. In addition, each electromagnetic coil may beenergized using dynamic current control to energize each coil at anappropriate time and bearing position to minimize wasted energy andinhibit the generated magnetic fields from affecting other bearings thatare entering or have already passed through the switch. Further, the useof the permanent magnet downstream of the coils facilitates guiding eachdiverted shoe into the diverting path in an energy efficient manner.

Therefore, in some embodiments, a shoe may be diverted in anelectromagnetic switch in part by sensing a portion of the shoeapproaching the electromagnetic switch, in response to sensing theportion of the shoe approaching the electromagnetic switch, energizing afirst electromagnetic coil while the shoe is adjacent the firstelectromagnetic coil to generate a first magnetic field urging the shoetowards the diverting path, and after energizing the firstelectromagnetic coil, energizing a second electromagnetic coilpositioned downstream of the first electromagnetic coil while the shoeis adjacent the second electromagnetic coil to generate a secondmagnetic field further urging the shoe towards the diverting path. Bydoing so, the shoe may be positioned adjacent a permanent magnetdisposed downstream of the second electromagnetic coil and proximate thediverting path such that a third magnetic field generated by thepermanent magnet further urges the shoe towards the diverting path.

Returning to FIG. 2, switch 120 also includes a separator 160, e.g.,formed of glass nylon or another suitable material, for separating thediverting and non-diverting paths, as well as a bearing bridge 162,formed of glass nylon or another suitable material, for engaging thebearing of each diverted shoe. A post diverter block 164 supportsbearing bridge 162 and a divert confirm sensor 166, e.g., a photo-eye orother suitable sensor supported by a mounting block 168 (FIG. 4), may bepositioned in the diverting path to confirm when a shoe is successfullydiverted into the diverting path. A non-divert confirm sensor (notshown) may also be used in some embodiments, while in other embodimentssensor 164 may be omitted.

In addition, with further reference to FIG. 4, one or more cooling fans170 or other cooling systems (e.g., liquid cooling systems) may be usedto cool coils 148, 150 during operation, as it will be appreciated thatcoils 148, 150 increase in resistance and thus decrease in efficiency astheir temperature increases. As such, control over coil temperatures maybe desirable in some embodiments.

Now turning to FIG. 6, an example control system 200 for electromagneticswitch 120 is illustrated in greater detail. Control system 200 includesa controller 202, which may include one or more processors 204 and oneor more memories 206, and which is configured to control a drive circuit208 powered by a power supply 210 to energize one or moreelectromagnetic coils (e.g., electromagnetic coil 148 as shown in FIG.6), e.g., responsive to signals output by pin and bearing sensors 144,146. Power supply 210 may be configured as a DC power supply thatapplies a direct current voltage across a pair of power input terminals,positive power input terminal 212 and ground power input terminal 214,and drive circuit 208 may be configured to apply a voltage across a pairof electromagnetic coil terminals 216, 218 to allow for electric currentto flow between power supply 210 and electromagnetic coil 148. In someembodiments, power supply 210 may provide about 170 VDC, and may includevarious power supply components such as regulators, AC/DC converters,filters, etc. as may be desired for a particular application and sourceof electrical power.

In the illustrated embodiment, drive circuit 208 includes an H-bridgeincluding four switches 220, 222, 224 and 226, each controlled bycontroller 202. Switches 220 and 222 form a first leg of the H-bridge,with switch 220 coupled between power input terminal 212 and coilterminal 216 and switch 222 coupled between power input terminal 214 andcoil terminal 216. Switches 224 and 226 form a second leg of theH-bridge, with switch 224 coupled between power input terminal 212 andcoil terminal 218 and switch 226 coupled between power input terminal214 and coil terminal 218.

Further, in the illustrated embodiment, each switch 220, 222, 224 and226 includes a parallel arrangement of a MOSFET 228, e.g., an N-channelMOSFET and a reverse-biased diode 230. Each MOSFET 228 includes a gate,a drain and a source, and the drains of the MOSFETs 228 for switches 220and 224 are coupled to power input terminal 212, while the sources ofthe MOSFETs 228 for switches 222 and 226 are coupled to power inputterminal 214. The source of the MOSFET 228 for switch 220 and the drainof the MOSFET 228 for switch 222 are coupled to coil terminal 216 andthe source of the MOSFET 228 for switch 224 and the drain of the MOSFET228 for switch 226 are coupled to coil terminal 218.

The gate of each MOSFET 228 is coupled to controller 202. In one state,a Forward Voltage state, the MOSFETs 228 of switches 220 and 226 areclosed while the MOSFETs 228 of switches 222 and 224 are opened toeffectively apply a positive voltage potential across coil terminals216, 218, thereby supplying current to energize electromagnetic coil148. In a second state, a Reverse Voltage state, the MOSFETs 228 ofswitches 220 and 226 are opened while the MOSFETs 228 of switches 222and 224 are closed to effectively apply a negative voltage potentialacross coil terminals 216, 218, thereby reversing current flow throughelectromagnetic coil 148, which as described in greater detail below,may be used to recapture or recover energy from the electromagneticcoil. In a third state, an Off/Disconnected state, the MOSFETs 228 ofall four switches are opened to shut off the electromagnetic coil. In afourth state, a Regenerative state, the MOSFET 228 of switch 220 isclosed and the MOSFETs of switches 222, 224 and 226 are opened to bothreverse current flow through the electromagnetic coil and to captureinductive spikes from the electromagnetic coil.

In order to recapture or recover energy from the electromagnetic coil,it may be desirable to include one or more capacitors or other energystorage device between electromagnetic coil 148 and DC power supply 210,e.g., polarized capacitor 232, which in the illustrated embodiment iscoupled in parallel with a ceramic or other appropriate capacitor 234for use in noise filtering. While capacitors 232, 234 are shownintermediate power supply 210 and the H-bridge of drive circuit 208 andcoupled across power input terminals 212, 214, it will be appreciatedthat one or both of the capacitors may be resident within or otherwisebe considered to be components of power supply 210 in other embodiments,or disposed elsewhere in control system 200.

Controller 202, as noted above, may include one or more processors 204and one or more memories 206, and each memory 206 may represent therandom access memory (RAM) devices comprising the main storage ofcontroller 202, as well as any supplemental levels of memory, e.g.,cache memories, non-volatile or backup memories (e.g., programmable orflash memories), read-only memories, etc. In addition, the memory may beconsidered to include memory storage physically located elsewhere incontroller 202, e.g., any cache memory in a processor in a processor204, as well as any storage capacity used as a virtual memory, e.g., asstored on a mass storage device or on another computer or electronicdevice coupled to controller 202. Controller 202 may also include one ormore mass storage devices, e.g., a floppy or other removable disk drive,a hard disk drive, a direct access storage device (DASD), an opticaldrive (e.g., a CD drive, a DVD drive, etc.), and/or a tape drive, amongothers. Furthermore, controller 202 may include an interface with one ormore networks (e.g., a LAN, a WAN, a wireless network, and/or theInternet, among others) to permit the communication of information tothe components in electromagnetic switch 120 as well as with othercomputers and electronic devices. Controller 202 operates under thecontrol of an operating system, kernel and/or firmware and executes orotherwise relies upon various computer software applications,components, programs, objects, modules, data structures, etc. Moreover,various applications, components, programs, objects, modules, etc. mayalso execute on one or more processors in another computer coupled tocontroller 202, e.g., in a distributed or client-server computingenvironment, whereby the processing required to implement the functionsof a computer program may be allocated to multiple computers over anetwork.

In general, the routines executed to implement the embodiments of theinvention, whether implemented as part of an operating system or aspecific application, component, program, object, module or sequence ofinstructions, or even a subset thereof, will be referred to herein as“computer program code,” or simply “program code.” Program codetypically comprises one or more instructions that are resident atvarious times in various memory and storage devices in a computer, andthat, when read and executed by one or more processors in a computer,cause that computer to perform the steps necessary to execute steps orelements embodying the various aspects of the invention. Moreover, whilethe invention has and hereinafter will be described in the context offully functioning controllers, computers and computer systems, thoseskilled in the art will appreciate that the various embodiments of theinvention are capable of being distributed as a program product in avariety of forms, and that the invention applies equally regardless ofthe particular type of computer readable media used to actually carryout the distribution.

Such computer readable media may include computer readable storage mediaand communication media. Computer readable storage media isnon-transitory in nature, and may include volatile and non-volatile, andremovable and non-removable media implemented in any method ortechnology for storage of information, such as computer-readableinstructions, data structures, program modules or other data. Computerreadable storage media may further include RAM, ROM, erasableprogrammable read-only memory (EPROM), electrically erasableprogrammable read-only memory (EEPROM), flash memory or other solidstate memory technology, CD-ROM, digital versatile disks (DVD), or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium that canbe used to store the desired information and which can be accessed bycontroller 202. Communication media may embody computer readableinstructions, data structures or other program modules. By way ofexample, and not limitation, communication media may include wired mediasuch as a wired network or direct-wired connection, and wireless mediasuch as acoustic, RF, infrared and other wireless media. Combinations ofany of the above may also be included within the scope of computerreadable media.

Various program code described hereinafter may be identified based uponthe application within which it is implemented in a specific embodimentof the invention. However, it should be appreciated that any particularprogram nomenclature that follows is used merely for convenience, andthus the invention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature. Furthermore,given the typically endless number of manners in which computer programsmay be organized into routines, procedures, methods, modules, objects,and the like, as well as the various manners in which programfunctionality may be allocated among various software layers that areresident within a typical computer (e.g., operating systems, libraries,API's, applications, applets, etc.), it should be appreciated that theinvention is not limited to the specific organization and allocation ofprogram functionality described herein.

It will also be appreciated that for the sake of simplifying theillustration of drive circuit 208 in FIG. 6 illustrates only thecomponents used to couple power supply 210 to electromagnetic coil 148.In order to drive electromagnetic coil 150, drive circuit 208 mayinclude a second H-bridge circuit configured similar to the arrangementillustrated in FIG. 6, and thus may include four additional switchessimilar to switches 220, 222, 224 and 226, coupled in parallel to theH-bridge formed by switches 220, 222, 224, and 226, and controlled byseparate control lines from controller 202. In this embodiment, bothcoils 148, 150 are driven by the same power supply 210 and utilize thesame capacitor 232 as energy storage. In other embodiments, however,coils 148, 150 may be driven by separate power supplies, may utilizedifferent drive circuits and/or may be controlled by differentcontrollers.

Now turning to FIG. 7, and with additional reference to FIG. 5, anenergization sequence for energizing coils 148, 150 in order to divert ashoe into a diverting path with electromagnetic switch 120 isillustrated in further detail. In particular, in some embodimentsconsistent with the invention, it is generally desirable to operate eachelectromagnetic coil 148, 150 in an energy efficient manner thatsupplies voltage and current to a coil such that the coil is energizedon a dynamic timing schedule based upon the speed of the shoe passingthrough the switch geometry. In such embodiments, when a coil isdeenergized (in this sense, the power to the coil is shutoff, but thecoil has not yet returned to its equilibrium “off” state), somepercentage of the current flowing out from the coil may be recapturedinto a charge storage device (e.g., capacitor 232 of FIG. 6), and thatstored energy may then be recirculated through the drive circuit againwhen the coil is reenergized for the next cycle. In this sense, a cyclemay be considered to be a period where the current passing through thecoil is raised to an acceptable level before the power is shutoff toallow the current to fall a small amount before being reenergized backto the acceptable level, and thereby maintaining an average hold-oncurrent during at least a portion of the energization. By doing so, thecurrent capacity of the electromagnetic coil is effectively artificiallyclipped, which in some embodiments may enable a low resistance coil,which would normally draw an immense amount of current, to be driven ina manner that enables current to flow through the coil quickly enoughyet at a reduced rate that is sufficient to generate the necessarycomplex current induced magnetic field that ultimately urges the pinand/or bearing of a shoe into a diverting path. This magnetic field maybe generated and deconstructed in a brief period of time such that thecreation, sustained field, and destruction events all occur while thetarget pin and/or bearing is still passing in front of the face of theelectromagnetic coil.

By capturing the reusable current flowing out from an electromagneticcoil in an expedited manner into a capacitive device, the amount ofenergy the coil is required to dissipate is reduced, and thus thetemperature of the coil remains lower. This lower temperature generallykeeps the internal DC resistance of the coil lower and allows the coilto maintain its original efficiency without wasting current as heat andRF energy due to a higher resistance as the temperature of the coilwould normally raise.

The recovery operation may be accomplished by the aforementioned drivecircuit incorporating an H-bridge configuration of switches capable ofcontrolling current flow in several different states: Forward Voltage,Reverse Voltage, Off/Disconnected, and Regenerative. The Forward Voltagestate (where switches 220 and 226 are on and switches 222 and 224 areoff) may be used to drive the electromagnetic coil to generate amagnetic field, the Reverse Voltage state (where switches 220 and 226are off and switches 222 and 224 are on) may be used to reverse currentflow through the electromagnetic coil at the end of energization, theOff/Disconnected state (where all switches are off) may be used to shutoff the electromagnetic coil, and the Regenerative state (where switch220 is on and switches 222, 224 and 226 are off) may be used to bothreverse current flow through the electromagnetic coil and to captureinductive spikes from the electromagnetic coil when maintaining thehold-on current during energization. By taking advantage of inductorcharacteristics and inductive spiking, the herein-described design mayenable excess charge to flow back to the positive potential of thecircuit's capacitors to improve overall energy efficiency within thecircuit. In the Regenerative state, for example, a further optimizationis provided over the reverse-bias diode, allowing for a greater captureof the inductive spike while also reducing the heat generated by theinductive spike by not needing to overcome the diode, and providing asubstantial power savings for high frequency switching.

Therefore, in some embodiments consistent with the invention, a shoe maybe diverted by an electromagnetic switch in part by energizing anelectromagnetic coil of the electromagnetic switch to generate amagnetic field urging the shoe towards the diverting path, and whilegenerating the magnetic field with the electromagnetic coil, alternatingbetween supplying electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil to recoverenergy from the electromagnetic coil. In some instances, as will becomemore apparent below, an electromagnetic coil may be energized in twoportions or phases, with the first portion or phase used to drive theelectromagnetic coil to ramp up electrical current supplied to the firstelectromagnetic coil to a peak current, and with the second portion orphase used to maintain an average hold-on current supplied to the firstelectromagnetic coil, in part by alternating between supplyingelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil.

Now turning to FIG. 7, and with additional reference to FIG. 5, anexample timing diagram is provided to illustrate the timing ofenergization for coils 148, 150 by controller 202. The timing diagramhas six different lines that illustrate the timing of differentcomponents of the sequence. The pin sensor line illustrates thedetection of a pin of a shoe approaching the electromagnetic switch,e.g., as sensed by pin sensor 144 discussed above (generallycorresponding to position P1 illustrated in FIG. 5), while the bearingsensor line illustrates the detection of a bearing of a shoe approachingthe electromagnetic switch, e.g., as sensed by pin sensor 146 discussedabove (generally corresponding to position P2 illustrated in FIG. 5).The first and second coil state lines represent the energization stateof each of coils 148, 150, e.g., whether a positive voltage is appliedacross each coil. The first and second coil current lines, in turn,represent the instantaneous current flowing through the respective coil148, 150 at any given time.

A number of control parameters used to drive each coil 148, 150according to the first and second coil state lines may be dynamicallydetermined based upon the sensed speed and position of a shoe, and theletters A-G are used to denote various aspects of the control.

The letter A represents the time between the rising edge of the pinsensor and the rising edge of the bearing sensor, which can be used tocalculate the speed that a shoe is moving, as well as a start time forinitiating an energization sequence for energizing each coil. In variousembodiments, various control parameters may be determined and/orcontrolled, including, for example, the start time and/or duration forenergizing each of coils 148, 150, the desired peak current to be pushedthrough each of coils 148, 150 (as it will be appreciated that higherspeeds will generally require more current to pull the shoe within thesmaller time envelopes), the desired average hold-on current maintainedafter applying the peak current (again, higher speeds generally requirea higher holding current), the shutoff time or duration that each coil148, 150 is no longer energized, and various characteristics of ahold-on current phase of the energization. The hold-on current phase,for example, may include alternating between supplying electricalcurrent to the electromagnetic coil and reversing current flow throughthe electromagnetic coil, and as such the control parameters may includeparameters such as a number of cycles to alternate between supplyingelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil, a frequency of alternatingbetween supplying electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil, a duration ofsupplying electrical current to the electromagnetic coil during eachcycle, and a duration of reversing current flow through theelectromagnetic coil during each cycle, among others. Additional controlparameters may include, for example, the durations of the peak currentand hold-on current phases, among other control parameters that will beapparent to those of ordinary skill having the benefit of the instantdisclosure.

The letter B represents the delay between the rising edge of the bearingsensor, and the start time for the energizing sequence for coil 148.

The letter C represents the initial start point and duration for thepeak current phase for each of coils 148, 150, which is timed so as toraise the respective coil 148, 150 to a desired peak current for a givenshoe speed. It will be appreciated that as the shoe speed increases, ahigher peak current may be desired, so the start point of the peakcurrent phase may be advanced to an earlier point in time in order toallow the coil to reach peak current when the pin and/or bearing of theshoe is directly adjacent the coil (generally corresponding to positionP3 for coil 148 and position P4 for coil 150 illustrated in FIG. 5).

The letter D represents the hold-on current phase duration, whichmaintains an approximation of a desired hold-on current passing throughthe coil for a predetermined length of time based at least in part onthe speed of the shoe passing through the switch. In one exampleembodiment, the number of on-off cycles in this time may be varieddirectly with the total length of this period, or alternatively, a fixednumber of cycles may be used, with the duration of each cycle (or theduration of the on and/or off portions of each cycle, designated byletters E and F in FIG. 7) varied appropriately.

The letter E represents a duration of an “ON” portion of each cycleduring the hold-on current phase of energization, while the letter Frepresents an inductive spike recovery time where the coil is no longerin an “ON” state, but is passing some of its charge back into thecapacitive storage system to be used during the next “ON” cycle due to areversal in current flow enabled by the associated drive circuit.

The letter G represents the length of time required for the current tocease flowing through the coil and for the corresponding electromagneticfield to decay to a negligible strength.

In the illustrated embodiment, the Forward Voltage state, where switches220 and 226 are on and switches 222 and 224 are off, is used during theC and E durations. The Regenerative state, where switch 220 is on andswitches 222, 224 and 226 are off, is used during the F durations. TheReverse Voltage state, where switches 222 and 224 are on and switches220 and 226 or off, is used during the G durations. In otherembodiments, some or all of the F and G durations may both use theRegenerative state or the Reverse Voltage state, and in someembodiments, the Regenerative state may be used for the G durations andthe Reverse Voltage state may be used for the F durations. Put anotherway, in some embodiments, the reversal of current in the electromagneticcoil while maintaining the hold-on current may be implemented by closingonly switch 220, while in other embodiments, the reversal of current inthe electromagnetic coil while maintaining the hold-on current may beimplemented by closing switches 222 and 224. Other switch configurationssuitable for reversing current flow through an electromagnetic coil maybe used in other embodiments.

It will be appreciated that the peak current and the hold-on current maybe selected in different embodiments in different manners, and in someembodiments, these values may be dependent upon speed or other factors.In some embodiments, it may be desirable for the hold-on current to bereduced relative to the peak current, e.g., about 75% of peak current insome embodiments. In addition, while other frequencies may be used forthe cycles of the hold-on current phase, in some embodiments a frequencyof about 10 kHz may be used. It will also be appreciated that differentparameters may be used for the different coils in some embodiments.

Returning to FIG. 5, it will be appreciated that for a shoe beingdiverted to the diverting path, after coils 148, 150 are energized,advancement of a shoe will desirably cause the bearing of the shoe toengage with permanent magnet 156 (generally corresponding to position P5illustrated in FIG. 5). The shoe then continues down the diverting path(generally corresponding to position P6 illustrated in FIG. 5) and iseventually confirmed as being successfully diverted when sensed bysensor 166 (generally corresponding to position P7 illustrated in FIG.5). The shoe then exits switch 120 and continues along divert guideangle 132 (generally corresponding to position P8 illustrated in FIG.5).

FIG. 8 next illustrates an example sequence of operations 300 performed,for example, by controller 202 to process a shoe approaching theelectromagnetic switch. First, in block 302, the controller awaits asignal from the pin sensor detecting a leading edge of the pin of theshoe. Next, in block 304, a determination is made as to whether the shoeshould be diverted (e.g., based upon whether a signal has been receivedindicating that the shoe is adjacent an article on conveyor that is tobe diverted to a destination associated with the electromagneticswitch). If not, control returns to block 302 to await the next shoe. Inaddition, it will be appreciated that the shoe will continue from theinput path to the non-diverting path and exit the switch without beingdiverted, and that if used, a non-divert permanent magnet may be used tomaintain the shoe in the non-diverting path.

If, however, the shoe is to be diverted, control passes to block 306 toawait sensing the bearing of the shoe, indicated by a signal generatedby the bearing sensor downstream of the pin sensor. Then, in block 308,the speed and position of the shoe may be calculated based upon thesensor inputs, and from the speed and/or position, a number of controlparameters may be calculated in blocks 310 and 312. In block 310, forexample, the speed of the shoe may be used to calculate desired peak andaverage hold-on currents. In block 312, the ramp up (peak current phase)start time and the duration and/or hold-on parameters may be calculatedfor each core, thereby establishing the control parameters forenergizing each coil when the shoe is positioned directly adjacent thecoil.

Block 314 then waits for the ramp up start time for the first coil, andthen drives the first coil based upon the calculated parameters toinitially ramp up to the desired peak current and then maintain areduced hold-on current by repeatedly reversing current flow through thefirst coil during the hold-on phase of energization. Thereafter, block316 waits for the ramp up start time for the second coil, and thendrives the second coil based upon the calculated parameters to initiallyramp up to the desired peak current and then maintain a reduced hold-oncurrent by repeatedly reversing current flow through the second coilduring the hold-on phase of energization.

Block 318 next optionally waits for a signal from a divert confirmsensor to confirm successful diversion of the shoe. In response to afailure to confirm, an error may be signaled or a corrective action maybe taken. Control then returns to block 302 to wait for the next shoe.It will also be appreciated that pitch of the shoes may be such thatmultiple shoes may be passing through a switch at any given time, so thetiming of various operations associated with different shoes may overlapin time in some embodiments.

Other embodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the presentinvention. Therefore the invention lies in the claims set forthhereinafter.

What is claimed is:
 1. A method of diverting a shoe on a conveyor withan electromagnetic switch configured to selectively direct the shoe froman input path to one of a non-diverting path and a diverting path, themethod comprising: energizing an electromagnetic coil of theelectromagnetic switch to generate a magnetic field urging the shoetowards the diverting path, wherein energizing the electromagnetic coilincludes supplying an electrical current to the electromagnetic coil;and while generating the magnetic field with the electromagnetic coil,alternating between supplying electrical current to the electromagneticcoil and reversing current flow through the electromagnetic coil torecover energy from the electromagnetic coil.
 2. The method of claim 1,further comprising receiving a direct current voltage across first andsecond power input terminals, wherein the electromagnetic coil includesfirst and second coil terminals, and wherein alternating betweensupplying the electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil includesswitching a drive circuit between a first state in which the first andsecond power input terminals are electrically coupled respectively tothe first and second coil terminals of the electromagnetic coil and asecond state in which the first power input terminal is electricallycoupled to one of the second and first coil terminals of theelectromagnetic coil to receive current flow from the electromagneticcoil.
 3. The method of claim 2, wherein the drive circuit includes anH-bridge circuit that couples the first and second power input terminalsto the first and second coil terminals of the electromagnetic coil. 4.The method of claim 3, wherein the H-bridge circuit includes first andsecond legs coupled in parallel to one another and coupled across thefirst and second power input terminals, the first leg including a firstswitch coupled between the first power input terminal and the first coilterminal and a second switch coupled between the second power inputterminal and the first coil terminal, and the second leg including athird switch coupled between the first power input terminal and thesecond coil terminal and a fourth switch coupled between the secondpower input terminal and the second coil terminal, wherein when in thefirst state, the first and fourth switches are closed and the second andthird switches are open such that the first coil terminal is coupled tothe first power input terminal through the first switch and the secondcoil terminal is coupled to the second power input terminal through thefourth switch.
 5. The method of claim 4, wherein when in the secondstate, the first switch is closed and the second, third and fourthswitches are open such that the first power input terminal is coupled tothe first coil terminal through the first switch and the second powerinput terminal is electrically isolated from the first and second coilterminals.
 6. The method of claim 4, wherein when in the second state,the second and third switches are closed and the first and fourthswitches are open such that the first coil terminal is coupled to thesecond power input terminal through the second switch and the secondcoil terminal is coupled to the first power input terminal through thethird switch.
 7. The method of claim 4, wherein each of the first,second, third, and fourth switches comprises a respective first, second,third and fourth MOSFET.
 8. The method of claim 7, wherein each of thefirst, second, third, and fourth MOSFETs comprises an N-channel MOSFETand includes a gate, a drain and a source, wherein each of the first,second, third, and fourth switches further comprises a respectivereverse biased diode coupled between the drain and the source thereof,and wherein the drains of the first and third MOSFETs are coupled to thefirst power input terminal, the sources of the second and fourth MOSFETsare coupled to the second power input terminal, the source of the firstMOSFET and the drain of the second MOSFET are coupled to the first coilterminal and the source of the third MOSFET and the drain of the fourthMOSFET are coupled to the second coil terminal.
 9. The method of claim8, wherein switching between the first and second states includesdriving the gates of the first and fourth MOSFETs during the first stateto close the first and fourth switches.
 10. The method of claim 9,wherein switching between the first and second states includes drivingonly the gate of the first MOSFET during the second state to close thefirst switch.
 11. The method of claim 9, wherein switching between thefirst and second states includes driving the gates of the second andthird MOSFETs during the second state to close the second and thirdswitches.
 12. The method of claim 2, wherein reversing current flowthrough the electromagnetic coil to recover energy from theelectromagnetic coil includes storing energy recovered from theelectromagnetic coil in at least one capacitor.
 13. The method of claim12, wherein the at least one capacitor is coupled across the first andsecond power input terminals.
 14. The method of claim 12, wherein the atleast one capacitor is disposed in a power supply coupled across thefirst and second power input terminals.
 15. The method of claim 1,further comprising, during a first portion of the energization of theelectromagnetic coil, driving the electromagnetic coil to a peakcurrent, wherein alternating between supplying the electrical current tothe electromagnetic coil and reversing current flow through theelectromagnetic coil is performed during a second portion of theenergization of the electromagnetic coil to drive the electromagneticcoil with a hold-on current.
 16. The method of claim 15, wherein thehold-on current is less than the peak current.
 17. The method of claim16, wherein the hold-on current is about 75 percent of the peak current.18. The method of claim 15, further comprising: sensing a portion of theshoe approaching the electromagnetic switch; and determining a starttime of the first portion of the energization of the electromagneticcoil in response to sensing the portion of the shoe approaching theelectromagnetic switch to cause the electromagnetic coil to reach thepeak current while the portion of the shoe is adjacent theelectromagnetic coil.
 19. The method of claim 18, wherein sensing theportion of the shoe approaching the electromagnetic switch includesdetermining a speed of the shoe approaching the electromagnetic switch.20. The method of claim 19, wherein determining the speed of the shoeapproaching the electromagnetic switch includes sensing the portion ofthe shoe approaching the electromagnetic switch at multiple positions.21. The method of claim 10, wherein the portion of the shoe includes apin and a bearing, and wherein sensing the portion of the shoeapproaching the electromagnetic switch at multiple positions includessensing one of the pin and the bearing at a first position among themultiple positions and sensing one of the pin and the bearing at asecond position among the multiple positions.
 22. The method of claim18, further comprising determining a duration of each of the first andsecond portions of the energization of the electromagnetic coil inresponse to sensing the portion of the shoe approaching theelectromagnetic switch.
 23. The method of claim 18, further comprisingdetermining a frequency of alternating between supplying the electricalcurrent to the electromagnetic coil and reversing current flow throughthe electromagnetic coil in response to sensing the portion of the shoeapproaching the electromagnetic switch.
 24. The method of claim 18,further comprising determining a number of cycles to alternate betweensupplying the electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil in response tosensing the portion of the shoe approaching the electromagnetic switch.25. An electromagnetic switch for selectively directing a shoe on aconveyor from an input path to one of a non-diverting path and adiverting path, the electromagnetic switch comprising: anelectromagnetic coil; and a drive circuit coupled to the electromagneticcoil, the drive circuit configured to energize the electromagnetic coilto generate a magnetic field urging the shoe towards the diverting path,wherein the drive circuit is further configured to, during energizationof the electromagnetic coil, alternate between supplying electricalcurrent to the electromagnetic coil and reversing current flow throughthe electromagnetic coil to recover energy from the electromagneticcoil.
 26. The electromagnetic switch of claim 25, wherein the drivecircuit includes first and second power input terminals across which issupplied a direct current voltage, wherein the electromagnetic coilincludes first and second coil terminals, and wherein the drive circuitis configured to alternate between supplying the electrical current tothe electromagnetic coil and reversing current flow through theelectromagnetic coil by switching between a first state in which thefirst and second power input terminals are electrically coupledrespectively to the first and second coil terminals of theelectromagnetic coil and a second state in which the first power inputterminal is electrically coupled to one of the second and first coilterminals of the electromagnetic coil to receive current flow from theelectromagnetic coil.
 27. The electromagnetic switch of claim 26,wherein the drive circuit includes an H-bridge circuit, the H-bridgecircuit including first and second legs coupled in parallel to oneanother and coupled across the first and second power input terminals,the first leg including a first switch coupled between the first powerinput terminal and the first coil terminal and a second switch coupledbetween the second power input terminal and the first coil terminal, andthe second leg including a third switch coupled between the first powerinput terminal and the second coil terminal and a fourth switch coupledbetween the second power input terminal and the second coil terminal,wherein when in the first state, the drive circuit closes the first andfourth switches and opens the second and third switches such that thefirst coil terminal is coupled to the first power input terminal throughthe first switch and the second coil terminal is coupled to the secondpower input terminal through the fourth switch.
 28. The electromagneticswitch of claim 27, wherein when in the second state, the first switchis closed and the second, third and fourth switches are open such thatthe first power input terminal is coupled to the first coil terminalthrough the first switch and the second power input terminal iselectrically isolated from the first and second coil terminals.
 29. Theelectromagnetic switch of claim 27, wherein when in the second state,the second and third switches are closed and the first and fourthswitches are open such that the first coil terminal is coupled to thesecond power input terminal through the second switch and the secondcoil terminal is coupled to the first power input terminal through thethird switch.
 30. The electromagnetic switch of claim 27, wherein eachof the first, second, third, and fourth switches comprises a respectivefirst, second, third and fourth N-channel MOSFET and includes a gate, adrain and a source, wherein each of the first, second, third, and fourthswitches further comprises a respective reverse biased diode coupledbetween the drain and the source thereof, and wherein the drains of thefirst and third N-channel MOSFETs are coupled to the first power inputterminal, the sources of the second and fourth N-channel MOSFETs arecoupled to the second power input terminal, the source of the firstN-channel MOSFET and the drain of the second N-channel MOSFET arecoupled to the first coil terminal and the source of the third N-channelMOSFET and the drain of the fourth N-channel MOSFET are coupled to thesecond coil terminal.
 31. The electromagnetic switch of claim 30,wherein the drive circuit is configured to switch between the first andsecond states by driving the gates of the first and fourth N-channelMOSFETs during the first state to close the first and fourth switches.32. The electromagnetic switch of claim 31, wherein the drive circuit isconfigured to switch between the first and second states by driving thegates of the first and fourth MOSFETs during the first state to closethe first and fourth switches.
 33. The electromagnetic switch of claim31, wherein the drive circuit is configured to switch between the firstand second states by driving only the gate of the first MOSFET duringthe second state to close the first switch.
 34. The electromagneticswitch of claim 30, further comprising a power supply coupled across thefirst and second power input terminals and at least one capacitorconfigured to store energy recovered from the electromagnetic coil whenin the second state.
 35. The electromagnetic switch of claim 25, furthercomprising a controller coupled to the drive circuit and configured to,during a first portion of the energization of the electromagnetic coil,cause the drive circuit to drive the electromagnetic coil to a peakcurrent, and during a second portion of the energization of theelectromagnetic coil, cause the drive circuit to alternate betweensupplying the electrical current to the electromagnetic coil andreversing current flow through the electromagnetic coil with a hold-oncurrent that is less than the peak current.
 36. The electromagneticswitch of claim 35, further comprising one or more sensors configured tosense a portion of the shoe approaching the electromagnetic switch,wherein the controller is configured to determine a start time of thefirst portion of the energization of the electromagnetic coil inresponse to sensing of the portion of the shoe approaching theelectromagnetic switch by the one or more sensors to cause theelectromagnetic coil to reach the peak current while the portion of theshoe is adjacent the electromagnetic coil.
 37. The electromagneticswitch of claim 36, wherein the one or more sensors includes multiplesensors disposed at multiple positions, and wherein the controller isfurther configured to determine a speed of the shoe approaching theelectromagnetic switch in response to the sensing of the portion of theshoe approaching the electromagnetic switch by the one or more sensors.38. The electromagnetic switch of claim 37, wherein the portion of theshoe includes a pin and a bearing, and wherein the multiple sensorsincludes a first sensor disposed at a first position and configured tosense one of the pin and the bearing and a second sensor disposed at asecond position and configured to sense one of the pin and the bearing.39. The electromagnetic switch of claim 36, wherein the controller isfurther configured to determine a duration of each of the first andsecond portions of the energization of the electromagnetic coil inresponse to the sensing of the portion of the shoe approaching theelectromagnetic switch by the one or more sensors.
 40. Theelectromagnetic switch of claim 36, wherein the controller is furtherconfigured to determine a frequency of alternating between supplying theelectrical current to the electromagnetic coil and reversing currentflow through the electromagnetic coil in response to the sensing of theportion of the shoe approaching the electromagnetic switch by the one ormore sensors.
 41. The electromagnetic switch of claim 36, wherein thecontroller is further configured to determine a number of cycles toalternate between supplying the electrical current to theelectromagnetic coil and reversing current flow through theelectromagnetic coil in response to the sensing of the portion of theshoe approaching the electromagnetic switch by the one or more sensors.42. A controller for an electromagnetic switch configured to selectivelydirect a shoe on a conveyor from an input path to one of a non-divertingpath and a diverting path, the controller comprising: one or moreprocessors; and program code executable by the one or more processorsto: energize an electromagnetic coil of the electromagnetic switch togenerate a magnetic field urging the shoe towards the diverting path,wherein the controller is configured to energize the electromagneticcoil by causing an electrical current to be supplied to theelectromagnetic coil; and while the electromagnetic coil is energized togenerate the magnetic field, alternate between causing the electricalcurrent to be supplied to the electromagnetic coil and causing currentflow to be reversed through the electromagnetic coil to recover energyfrom the electromagnetic coil.